cmd: Add optional json format to inspect command output

[detsch]

@mike-sul here is an example output. My priority was to get something out to unblock the new tests, I'm sure you will have suggestions for improvements in the json format. "indexes" is particularly not a good name IMO.

Also, we may want to move part of the new code to pkg/compose/app.go

{
  "name": "shellhttpd_base_10000",
  "ref": "hub.foundries.io/detsch-temp-test-1/shellhttpd_base_10000@sha256:643ec5ca445dcccba14f3ce704f6b7d4ad80756047dbcee4fd1ab938a10a5a41",
  "meta": {
    "type": "app meta",
    "digest": "sha256:d0f98c59b144cd1f769074d64d483fa267150a30043f63a5a4ebf8646493df67",
    "size": 294
  },
  "index": {
    "type": "app index",
    "digest": "sha256:247d5eb89ba605f426455a5238510d166595ab520bad3dfdcae5ae6219b2eeeb",
    "size": 757
  },
  "bundle": {
    "type": "app bundle",
    "digest": "sha256:66946ccde0f071bbbd49d5e5bf2d0c27a1a8500b683ab3800429255c15c26f3a",
    "size": 1039
  },
  "indexes": [
    {
      "index": {
        "type": "index",
        "digest": "sha256:98e4fcf4df5e67ec7dcb4efb83d4d5b3dc8ca85a1fc792d4a4806e92e26228c4",
        "size": 433
      },
      "manifest": {
        "type": "manifest",
        "digest": "sha256:bb28ee97ff89067d391e838cef15f80dd77659f4d5f23f2af15f48998428c0e8",
        "size": 696
      },
      "blobs": [
        {
          "type": "config",
          "digest": "sha256:312c4b1d9d21667e7483409396b8a8c3deb3236063471c92245fba4970141e6e",
          "size": 808
        },
        {
          "type": "layer",
          "digest": "sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870",
          "size": 3642247
        },
        {
          "type": "layer",
          "digest": "sha256:616b7f571c8ee24772b38ccfb5418fccee5bdf443af4f89b2f76e48cd9b3af09",
          "size": 387
        }
      ]
    },
    {
      "index": {
        "type": "index",
        "digest": "sha256:98e4fcf4df5e67ec7dcb4efb83d4d5b3dc8ca85a1fc792d4a4806e92e26228c4",
        "size": 433
      },
      "manifest": {
        "type": "manifest",
        "digest": "sha256:bb28ee97ff89067d391e838cef15f80dd77659f4d5f23f2af15f48998428c0e8",
        "size": 696
      },
      "blobs": [
        {
          "type": "config",
          "digest": "sha256:312c4b1d9d21667e7483409396b8a8c3deb3236063471c92245fba4970141e6e",
          "size": 808
        },
        {
          "type": "layer",
          "digest": "sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870",
          "size": 3642247
        },
        {
          "type": "layer",
          "digest": "sha256:616b7f571c8ee24772b38ccfb5418fccee5bdf443af4f89b2f76e48cd9b3af09",
          "size": 387
        }
      ]
    },
    {
      "index": {
        "type": "index",
        "digest": "sha256:98e4fcf4df5e67ec7dcb4efb83d4d5b3dc8ca85a1fc792d4a4806e92e26228c4",
        "size": 433
      },
      "manifest": {
        "type": "manifest",
        "digest": "sha256:bb28ee97ff89067d391e838cef15f80dd77659f4d5f23f2af15f48998428c0e8",
        "size": 696
      },
      "blobs": [
        {
          "type": "config",
          "digest": "sha256:312c4b1d9d21667e7483409396b8a8c3deb3236063471c92245fba4970141e6e",
          "size": 808
        },
        {
          "type": "layer",
          "digest": "sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870",
          "size": 3642247
        },
        {
          "type": "layer",
          "digest": "sha256:616b7f571c8ee24772b38ccfb5418fccee5bdf443af4f89b2f76e48cd9b3af09",
          "size": 387
        }
      ]
    },
    {
      "index": {
        "type": "index",
        "digest": "sha256:98e4fcf4df5e67ec7dcb4efb83d4d5b3dc8ca85a1fc792d4a4806e92e26228c4",
        "size": 433
      },
      "manifest": {
        "type": "manifest",
        "digest": "sha256:bb28ee97ff89067d391e838cef15f80dd77659f4d5f23f2af15f48998428c0e8",
        "size": 696
      },
      "blobs": [
        {
          "type": "config",
          "digest": "sha256:312c4b1d9d21667e7483409396b8a8c3deb3236063471c92245fba4970141e6e",
          "size": 808
        },
        {
          "type": "layer",
          "digest": "sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870",
          "size": 3642247
        },
        {
          "type": "layer",
          "digest": "sha256:616b7f571c8ee24772b38ccfb5418fccee5bdf443af4f89b2f76e48cd9b3af09",
          "size": 387
        }
      ]
    },
    {
      "index": {
        "type": "index",
        "digest": "sha256:98e4fcf4df5e67ec7dcb4efb83d4d5b3dc8ca85a1fc792d4a4806e92e26228c4",
        "size": 433
      },
      "manifest": {
        "type": "manifest",
        "digest": "sha256:bb28ee97ff89067d391e838cef15f80dd77659f4d5f23f2af15f48998428c0e8",
        "size": 696
      },
      "blobs": [
        {
          "type": "config",
          "digest": "sha256:312c4b1d9d21667e7483409396b8a8c3deb3236063471c92245fba4970141e6e",
          "size": 808
        },
        {
          "type": "layer",
          "digest": "sha256:f18232174bc91741fdf3da96d85011092101a032a93a388b79e99e69c2d5c870",
          "size": 3642247
        },
        {
          "type": "layer",
          "digest": "sha256:616b7f571c8ee24772b38ccfb5418fccee5bdf443af4f89b2f76e48cd9b3af09",
          "size": 387
        }
      ]
    }
  ]
}
` ``